In injection molding, hot melt is injected from an injection molding machine into the tool (injection mold), either directly or by way of a hot-passage manifold system by means of a hot-passage nozzle. The tool consists of an injection side, accommodating the hot-passage nozzle, in which the outer mold (cavity) of the synthetic part to be molded is typically located, and an injector side with the inner mold (core). The region in which the hot-passage nozzle meets the tool and the synthetic part is referred to as the ‘initial cut.’ The anterior, tool-side part of the hot-passage nozzle with the initial cut region extends, in injection molding, into a recess of the tool. In the posterior region, the nozzle is supported axially on the hot-passage manifold block and is fixed to the anterior, initial cut part by means of precision seal in the tool. There, the nozzle is exposed to high mechanical and thermal stresses.
Since the initial cut region of the nozzle is consequently subject to rapid wear, it is not configured as an integral part of the hot-passage nozzle, but as a replaceable tool insert. Of importance in injection molding is a thermal separation between nozzle and tool. The melt injected into the tool is to solidify quickly, while the melt retained in the tip of the nozzle is to remain liquid. Hence it is known that the tool insert may be cooled by means of a coolant, for example water. For this purpose, diametrally opposed in the tool, a supply and a discharge passage for a coolant supplied to the tool open at the wall of the generally cylindrical recess in the tool, and the tool insert is provided at its outside on the level of the two said passages with an annular groove by way of which the coolant can flow from the supply passage to the discharge passage.